Actually, they do not need the keys, that is the point of lite account, they can just sign in with the gmail and they will not need keys unless you are trying to onboard them to other Hive dapps, which you are not, you are bringing them only to Inleo.

They don't even need the keys to do any exchange because all you do is send the Hive with a memo to the exchange account.

And for the app part, they can have de version of the site that gets saved as an icon on the phone, but I do thing having an app for the normies would be helpful